Characterization of eosinophil adhesion to TNF-α-activated endothelium under flow conditions: α₄ Integrins mediate initial attachment, and E- selectin mediates rolling

The multistep model of leukocyte adhesion reveals that selectins mediate rolling interactions and that integrins mediate firm adhesion processes. In this study, the interaction between eosinophils and TNF-α-activated HUVEC (second or third passage) was studied under flow conditions (0.8 and 3.2 dynes/cm²). Especially the role of α₄ integrins on eosinophils and E- selectin on HUVEC was studied. Inhibition of the integrin α₄ chain on eosinophils reduced the number of firmly adhered resting eosinophils to TNF- α-stimulated endothelium by 43% whereas the percentage rolling cells increased 2.2-fold compared with untreated control eosinophils. Blocking of E-selectin on the endothelium reduced the number of adherent eosinophils by only 23% and 16%. In this situation, however, hardly any rolling adhesion was observed, and the few rolling cells showed a low rolling velocity. Blocking both α₄ integrin on eosinophils and E-selectin on HUVEC reduced the number of adhered eosinophils by 95%. P-selectin did not significantly participate in eosinophil adhesion to TNF-α-activated HUVEC. Inhibition of both α₄ integrins and β₂ integrins on eosinophils resulted in a reduction of adhered cells by 65% and a 3-fold increase in percentage rolling cells. Taken together, these results clearly show that resting eosinophils preferentially use constitutively active α₄ integrins (α₄β₁, α₄β₇) for the first attachment to TNF-α-activated HUVEC. In addition, α₄ integrins and E- selectin work synergistically in eosinophil adherence to TNF-α-activated HUVEC. Although E-selectin is important for eosinophil rolling under these conditions, P-selectin plays only a minor role.